The present invention relates to a circuit for deriving a temperature-independent square-wave signal from a measurement signal which consists of a DC component and an AC component and which is taken across a magneto-resistor exposed to an alternative magnetic field.
A circuit with a bridge circuit consisting of four magneto-resistors is described in "Elektronik", No. 10, May 17th, 1985, pp. 99 to 101, where on p. 100 an operational amplifier is used as a signal amplifier, and a Schmitt-trigger-connected operational amplifier as a pulse shaper. The supply voltage is assumed to be constant, and temperature compensation is effected by a PTC resistor via an additional amplifier and a voltage divider. Each of the leads to the signal amplifier contains a resistor for eliminating any temperature dependence of the gain. The prior art circuit requires at least four terminal leads, namely two for the supply voltage and two for the output signal.